1. Field of the Invention
This invention relates to optical systems, and more specifically, to a swept wavelength optical system that incorporates a coherent interference in both a reference path and a measurement path.
2. Description of the Related Art
Optical measurement systems, optical storage and retrieval systems and other optical systems may be limited by many factors, including illumination beam size, diffraction limit, detector noise, and resolution. The above-incorporated patent application discloses swept-wavelength techniques for enhancing the performance of a variety of optical systems and improving the resolution and sensitivity of optical technologies disclosed therein. It would be further desirable to improve the performance of the systems disclosed in the above-referenced patent application, as well as other optical systems, in order to further improve their performance.
The system phase accuracy requirement in some measurement applications requires the wavelength control to meet or exceed 0.01% of the wavelength. Further, the resonator further multiplies deviations in phase by the cavity length. With a resonator length of 10000λ, phase control to 0.01% of the wavelength dictates control of the illumination wavelength to within 1 part in a hundred million or better, which is difficult or impossible to stably achieve while maintaining high speed operation by using a tunable illumination source and feedback loop. The above-incorporated patent application overcomes this barrier by providing a swept-wavelength system and method, that do not require a phase-stable source. However, variations in wavelength in terms of wavelength offset, drift and jitter are difficult to manage in a swept-wavelength measurement system. In particular, sufficiently agile sources are even more difficult to stabilize than fixed-wavelength sources due to the rapidly tunable nature of the source, as any cavity used to stabilize or otherwise operate the laser must be tuned in the wavelength sweeping process or must be sufficiently broadband that stabilization is essentially not provided by the cavity. Further, in an electrically swept illumination subsystem such as those employing an electrically-tunable laser diode, electrical noise in the control system or at the junction itself provides phase variation or jitter.
Therefore, it would be desirable to provide an alternative method and system for swept-wavelength measurement that overcomes the stability limitations of the illumination source.